Investment casting is a process for casting precision metal "parts," such as jewelry components, denture components and precision machinery parts.
In an investment casting process, patterns or models formed of a special wax (or resin or like material) are embedded in a refractory investment mold, usually by dip-coating the wax pattern several times in a liquid suspension of a fine-grained refractory. After the refractory dries, the wax is removed, leaving a thin-walled refractory shell for use as a ceramic mold for the metallic parts.
In preparing the ceramic molds, it is common to dip-coat several individual wax patterns at one time. Each of the patterns is attached to a vertical wax support member and the resulting assemblage is repeatedly dip-coated. After dip-coating, a single investment mold structure is created, made up of several individual mold units. The investment mold structure has a nearly continuous ceramic exterior with a single sprue opening in its base. The interior of this structure is waxed-filled with the wax patterns disposed within the contours of the individual molds. A cross-sectional view of a typical investment mold structure is shown in FIG. 7.
After this investment mold structure is created, the wax must be removed from the interior of the structure. Preferably the wax is recovered, treated to remove process impurities and then reused to make new patterns.
Removing the wax from the interior of the mold structure is generally accomplished by heating the mold structure and allowing the molten wax to flow out of the structure through the sprue opening. The mold structure must be heated rapidly. If the mold structure is heated slowly, the more rapidly expanding wax will crack the less rapidly expanding ceramic shell.
In most of the older investment cast processes, the mold structure is heated in a high pressure autoclave. However, the recovered wax from an autoclave-heated unit is mixed with the autoclave steam condensate, making recovery and treatment of the wax difficult and expensive. Furthermore, heating the mold structure in an autoclave does not always accomplish the removal of all of the wax as quickly and as completely as frequently desired. Still further, high pressure autoclaves are expensive to purchase, complex to maintain and relatively dangerous to operate.
To avoid these problems, mold structures are increasingly being dewaxed by a "flash fire" dewaxing process. In such a process, the investment mold structure is rapidly heated to a temperature in excess of 1000.degree. F. in a convection furnace. The wax is thereby rapidly and completely driven from the mold structure. Problems, however, remain with respect to recovering the wax. At the high temperature and oxygen-rich environment present within the flash fire furnace, the wax tends to exit the sprue hole in a flaming state. The flaming wax must be quickly and safely quenched before the wax can be recycled. In a typical prior art quenching method, the flaming wax is allowed to drop through a grating in the furnace floor and is extinguished in a water bath. However, this again introduces water into the recovered wax, making it difficult and expensive to purify the wax for reuse.
Accordingly, there is a need for an extinguishing method and apparatus usable in the flash fire dewaxing process which is inexpensive, safe and simple to use, but which does not use a water quench or other method which would make difficult the purification and reuse of the recovered wax.